Fuel composition which combusts instantaneously, method and plant therefor

ABSTRACT

Fuel composition which combusts instantaneously, comprising from 40 to 95% by weight of an instantaneously combusting fossil fuel and from 60 to 5% by weight of a non-fossil solid fuel chosen from the group comprising urban solid waste, elastomeric and non-elastomeric polymer materials and mixtures thereof, this fuel being suitably treated so as to be instantaneously combustible. Method and plant for the instantaneous combustion of the said composition.

This application is a continuation of U.S. patent application Ser. No.10/077,889 (now abandoned), filed Feb. 20, 2002, which is continuationof U.S. patent application Ser. No. 09/301,309, filed Apr. 29, 1999 (nowU.S. Pat. No. 6,375,691), which claims benefit of U.S. ProvisionalApplication No. 60/088,435, filed Jun. 8, 1998, and which claims benefitof priority to European Patent Application No. 98830262.6, filed Apr.30, 1998, the contents of all of which are incorporated herein byreference.

The present invention relates to a fuel composition which combustsinstantaneously, to an instantaneous combustion method which uses thesaid composition and to a plant for carrying out the said method.

More particularly, the present invention relates to a fuel compositionwhich combusts instantaneously, comprising a fossil fuel and anon-fossil solid fuel (NFSF) chosen from the group comprising urbansolid waste (USW), elastomeric and non-elastomeric polymer materials,and mixtures thereof.

Many methods have up to now been proposed for destroying and/orrecovering, at least partly, used plastic wrapping materials, tyresand/or urban solid waste.

However, the problem is very complex since the nature and composition ofurban solid waste varies from one place to another and from day to day,and on account of the presence of putrefiable organic waste.

A number of the methods proposed to date envisage the removal of theputrefiable organic phase from the solid products, which can then bedried, ground and agglomerated. Generally, the agglomeration is carriedout by compression into granules or tiles which are then destroyed bycombustion in ovens with a moving grate or with a rotating drum in whichthey remain in the high-temperature zone in which the combustion takesplace, for a period which is sufficient to obtain virtually completecombustion of the combustible mass. This duration, which can readily becontrolled and calculated by dividing the length of the path traveled bythe said mass in the said combustion zone by the throughput speed, is atleast 1 minute, preferably at least 3 minutes, generally 5 minutes ormore.

In the Applicant's view, a drawback of these methods is that thesegranules or tiles cannot be used to feed instantaneous-combustionburners. Yet another drawback is that the preparation of granules andtiles involves a number of stages, such as a compression stage, whichinvolve a certain expenditure of energy and thus increase the costs,making the above-mentioned known methods uneconomical.

A fuel composition has now been found which is produced while avoidingthe formation of agglomerates and which makes it possible to economizeon large amounts of fossil fuels in the production of energy.

In its first aspect, the present invention relates to a fuel compositionwhich combusts instantaneously, comprising from 40 to 95% by weight ofan instantaneously combustible fossil fuel and from 60 to 5% by weightof a non-fossil solid fuel (NFSF) chosen from the group comprising urbansolid waste, elastomeric and non-elastomeric polymer materials andmixtures thereof, this fuel being suitably treated so as to beinstantaneously combustible.

Preferably, the amount of the said instantaneously combustible fossilfuel is between 50 and 90% by weight and that of the NFSF is between 50and 10% by weight. Even more preferably, the amount of the saidinstantaneously combustible fossil fuel is between 60 and 80% by weightand that of the NFSF is between 40 and 20% by weight.

Throughout the present description and the claims, the term“instantaneous combustion” is used to indicate a combustion whichincludes the combustion of at least 90% by weight of the fuel materialfed into a burner in less than 10 seconds, preferably less than 5seconds, even more preferably less than 3 seconds.

Typical examples of instantaneously combustible fossil fuels aremethane, fuel oil, which may be in emulsion form, and fossil coal dust,which may be in the form of an aqueous suspension.

Typical examples of processing to which urban solid waste is subjectedbefore it can be used as instantaneously combustible NFSF comprise, in anon-limiting manner, removal of any putrefiable organic compounds and ofany metals, drying, grinding and screening. The urban solid waste thusprocessed will be referred to hereinbelow as USW. In the case ofelastomeric and non-elastomeric polymer materials, suitable processingcomprises, in a non-limiting manner, removal of any metals, drying,grinding and screening.

Preferred examples of fuel compositions which are instantaneouslycombustible according to the present invention are:

coal dust+USW,

coal dust+non-elastomeric polymer material,

coal dust+USW+non-elastomeric polymer material,

coal dust+usw+elastomeric polymer material,

coal dust+non-elastomeric polymer material+elastomeric polymer material,

coal dust+USW+non-elastomeric polymer material+elastomeric polymermaterial,

methane gas+USW,

methane gas+non-elastomeric polymer material,

methane gas+USW+non-elastomeric polymer material,

methane gas+USW+elastomeric polymer material,

methane gas+non-elastomeric polymer material+elastomeric polymermaterial,

methane gas+USW+non-elastomeric polymer material+elastomeric polymermaterial.

A typical example of a suitable non-fossil solid fuel compositioncomprising USW and elastomeric and non-elastomeric polymer materials isdescribed in the Applicant's Italian patent application No. M197A 02890of 30 Dec. 1997.

Typically, the non-fossil solid fuel composition of the abovementionedItalian patent application No. M197A 02890 comprises a first fractionconsisting of USW, a second fraction consisting of elastomeric materialand a third fraction consisting of non-elastomeric polymer material.Preferably, the composition has an apparent density is equal to or lessthan 0.6 g/cm³ and the amount of each of the three fractions ispreselected as a function of the desired calorific power. Typically thevalue of the apparent density is of from 0.2 to 0.6 g/cm³ and,preferably, of from 0.3 to 0.5.

One of the surprising properties of NFSF, observed during theexperimental tests described later, is that it behaves like an ordinaryinstantaneously combustible solid fuel of average calorific power. Ithas also been observed that efficient grinding and/or shredding of itscomponents to preset values makes it possible to reduce the content ofnon-combusted materials both in the heavy ash and in the fly ash,bringing this content to levels similar to those of the fossil fuel.

In general, the process for preparing the solid fuel composition of theabovementioned Italian patent application No. M197A 02890 comprises thefollowing stages:

a) an urban solid waste is processed in order to remove

a₁) the putrefiable organic fraction by screening,

a₂) ferrous materials, using a magnetic separator,

a₃) aluminium, using an eddy-current magnet,

b) the fraction of urban solid waste thus obtained is shredded,

c) a waste material consisting of non-elastomeric polymer material isshredded,

d) the abovementioned fractions of urban solid waste and ofnon-elastomeric polymer material shredded are dried to a moisturecontent of less than or equal to 10%,

e) the abovementioned fractions are ground,

f) an elastomeric material is ground and stripped of any ferrousmaterial associated therewith,

g) the abovementioned ground fractions are mixed together in a weightratio which is predetermined as a function of the desired calorificpower.

Examples of suitable elastomeric materials are used tyres. Examples ofsuitable non-elastomeric polymer materials are packaging and wrappingmade of thermoplastic and/or thermosetting materials. Typical examplesof thermoplastic materials mainly used in the production of wrappingmaterial are: PE, LDPE, HDPE, PP. PET, polystyrene, ethylene/C4-C12α-olefin copolymers, vinyl polymers and copolymers, and the like.

In its second aspect, the present invention relates to a fuelcomposition which combusts instantaneously, comprising from 40 to 95% byweight of an instantaneously combusting fossil fuel and from 60 to 5% byweight of particles smaller than 1 mesh (15 mm) in size of a fuelmaterial chosen from the group comprising USW, elastomeric andnon-elastomeric polymer materials, and mixtures thereof.

Preferably, at least 90% by weight of the abovementioned particles aresmaller than 2 mesh (7.5 mm) in size. Even more preferably, at least 50%by weight of the abovementioned particles are smaller than 4 mesh (3.75mm) in size.

Within the said composition, the granules of elastomeric polymer, ifpresent, are less than 5 mm in size.

The relatively large size of the NFSF particles constitutes an entirelyunexpected characteristic of the present invention. The reason for thisis that traditional instantaneously combusting fuel materials consist ofgaseous and liquid fossil fuels. However, a solid fossil fuel, such ascoal, is suitable for use as an instantaneously combusting fuel materialonly after it has been very finely ground until 99% of the particlesthereof are less than 100 mesh (0.15 mm) in size and 70% of theseparticles are less than 200 mesh (0.075 mm) in size. Thus, it was notforeseeable that NFSF would be suitable for instantaneous combustioneven though its particles are at least 50 times as large as those ofcoal dust.

Moreover, it was considered that the essential element had to be thesize of the elastomeric polymer granules and that they had to be similarin size to that of granules of coal dust. However, it was found,surprisingly, that it is sufficient for the elastomeric polymer granulesto be less than 5 mm in size.

Furthermore, in the case of the composition which constitutes the secondaspect of the invention, the amount of the said instantaneouslycombusting fossil fuel is preferably between 50 and 90% by weight andthat of the said fuel material is between 50 and 10% by weight. Evenmore preferably, the amount of the said instantaneously combustingfossil fuel is between 60 and 80% by weight and that of the said fuelmaterial is between 40 and 20% by weight.

A typical example of a suitable non-fossil solid fuel compositioncomprising USW and elastomeric and non-elastomeric polymer materials andof a method for producing it is described in the abovementioned Italianpatent application No. M197A 02890.

In a preferred embodiment of the present invention, the fuel materialchosen from the group comprising USW, elastomeric and non-elastomericpolymer materials and mixtures thereof consists of a mixture comprisingfrom 40 to 80% by weight of dry urban solid waste, from 10 to 50% byweight of elastomeric material and from 10 to 50% by weight ofnon-elastomeric polymer material. Even more preferably, this mixturecomprises from 60 to 80% by weight of dry urban solid waste, 10 to 30%by weight of elastomeric material and from 10 to 30% by weight ofnon-elastomeric polymer material.

In its third aspect, the present invention relates to a combustionmethod in which the flame of a burner of an instantaneous-combustionboiler is fed with a flow of instantaneously combusting fuel materialcomprising from 40 to 95% by weight of an instantaneously combustingfossil fuel and from 60 to 5% by weight of a fuel material chosen fromthe group comprising USW, elastomeric and non-elastomeric polymermaterials and mixtures thereof, which has been suitably treated so as tobe instantaneously combustible.

In a preferred embodiment, the said fossil fuel is fed through a burnerof known type, while the instantaneously combusting non-fossil fuel isfed into the region of the boiler known as the “fire area”, i.e. theregion of the boiler in which the temperature is above 1400° C.Generally, the temperature of the fire area is between 1500 and 2000° C.

Typically, the said fuel material is instantaneously combustible when itconsists of particles less than 1 mesh (15 mm) in size. Preferably, atleast 90% by weight of the abovementioned particles are less than 2 mesh(7.5 mm) in size. Even more preferably, at least 50% by weight of theabove-mentioned particles are less than 4 mesh (3.75 mm) in size. Theelastic polymer, if present, is preferably in the form of granules lessthan 5 mm in size.

Preferably, the flow of instantaneously corn-busting fuel material usedin the combustion method according to the present invention comprisesfrom 50 to 80% by weight of instantaneously combusting fossil fuel andfrom 50 to 20% by weight of fuel material chosen from the groupcomprising USW, elastomeric and nonelastomeric polymer materials andmixtures thereof. Even more preferably, the amount of the saidinstantaneously combusting fossil fuel is between 60% and 80% by weightand that of the said fuel material is between 40 and 20% by weight.

The method of the present invention has proved to be particularlysuitable for running power plants, i.e. plants generally dedicated tothe production of steam for the production of electrical energy and/orfor remote heating, and which produce an amount of steam greater than 40thermal megawatts (tMW). Generally, the said power plants are consideredsmall when they produce less than 50 tMW, medium-sized when they producefrom 50 to 500 tMW and big when they produce more than 500 tMW.

In another embodiment thereof, the combustion method of the presentinvention comprises feeding an instantaneously combusting fuel material,comprising at least one fossil fuel and a non-fossil fuel chosen fromthe group comprising USW, elastomeric and non-elastomeric polymermaterials and mixtures thereof, into a zone of a boiler which is at atemperature such that the level of non-combusted materials in the heavyash is maintained at less than 50% by weight.

In another embodiment thereof, the combustion method of the presentinvention comprises feeding a boiler with an instantaneously combustingfuel material comprising at least one fossil fuel and a non-fossil fuelchosen from the group comprising USW, elastomeric and non-elastomericpolymer materials and mixtures thereof, in which the particle size ofthe said non-fossil fuel has been predetermined such that the level ofthe non-combusted materials in the heavy ash is maintained at less than50% by weight.

In its fourth aspect, the present invention thus relates to a plant forthe instantaneous combustion of at least one instantaneously combustingfossil fuel, comprising a boiler, at least one burner, a combustion zoneand a system for feeding in at least one said instantaneously combustingfossil fuel, characterized in that it also comprises a device forfeeding a non-fossil solid fuel (NFSF) into the said combustion zone.

According to two preferred embodiments of the present invention, thesaid .NFSF supply device is of the mechanical or pneumatic type. Inparticular, the mechanical supply device is preferably an Archimedeanscrew device.

The invention will now be illustrated in greater detail by means of thedescription of experimental tests and figures, which are given purely asexamples and should thus not be interpreted as limiting the scope of thepresent invention in any way.

In the attached figures

FIG. 1 is a diagram which shows the values of nitrogen oxides (NO_(x)),of CO and of non-combusted materials which are formed as the amount ofoxygen is varied in a combustion test carried out with coal dust alone;

FIG. 2 is a diagram which shows the values of heavy ash (HA) which areformed in a combustion test carried out with carbon dust alone, incomparison with two co-combustion tests carried out with various amountsof coal dust and of NFSF;

FIG. 3 is a diagram which shows the values of noncombusted materialsfound in the heavy ash in a combustion test carried out with coal dustalone, in comparison with two co-combustion tests carried out withvarious amounts of coal dust and of NFSF;

FIG. 4 is a diagram which shows the values of nitrogen oxides (NO_(x)),of CO and of non-combusted materials which are formed in a combustiontest carried out with coal dust alone, in comparison with a coaldust/NFSF co-combustion test;

FIG. 5 is a diagram which shows the values of SO₂ which is formed in acombustion test carried out with coal dust alone, in comparison with acoal dust/NFSF co-combustion test;

FIG. 6 is a diagram which shows the values of fly ash which is formed ina combustion test carried out with coal dust alone, in comparison with acoal dust/NFSF co-combustion test;

FIG. 7 is a schematic representation of a power plant for the combustionof an instantaneously combusting fuel material of the present invention;

FIG. 8 is a schematic representation of a first system for supplying aninstantaneously combusting fuel material of the present invention intoan experimental boiler;

FIG. 9 is a schematic representation of a second system for supplying aninstantaneously combusting fuel material of the present invention intoan experimental boiler.

In FIGS. 7-9, the same numbers correspond to the same components.

FIG. 7 shows, schematically, a typical power plant which is suitable forgenerating steam by means of the instantaneous combustion of the fuelmaterial of the present invention.

This plant comprises a steam-generating boiler (18A) which has severalburners (12). These burners can be, for example, of the type illustratedschematically in FIGS. 8 and 9 in which they are labelled with the samereference number 12.

The general structure of the boiler, or steam generator, (18A) is of aknown type and is briefly described hereinbelow with particularreference to the specific properties which are useful for illustratingthe present invention.

Typically, the boiler (18A) has a plurality of burners (12) (for exampleup to 60), the precise number of the said burners (12) beingpredetermined from one instance to another depending on the capacity ofthe boiler (18A). The said burners (12) can be arranged on a singlewall, on two opposite walls (as illustrated in FIG. 7) or in the cornersof the combustion zone (11), also called fire zone. The configuration ofthe said array of burners (12) will be preselected from one instance toanother depending on criteria which are well known to those skilled inthe art, as a function of the predetermined thermal properties for thecombustion zone (11).

In the combustion zone (11) defined in correspondence with the burners(12), the flames generated by these burners (12) maintain a temperatureof typically between 1500 and 2000° C.

Structures and/or members capable of collecting and removing the ash arepresent at the bottom of the boiler. Typical examples of the saidstructures and members are a hopper (13) for collecting the ash and aconveyor belt (19) for removing it.

In the top part of the boiler (18A), in relation to a narrowing of thepassage cross-section usually referred to as the “nose of the boiler”(18C), the vapours arising from the combustion zone (11) arrive at avapour exit zone (18B), in which the vapours have a temperature of about1150-1250° C. Next, the vapours cross a zone, referred to collectivelyas the “convective bank”, which comprises a plurality of heat exchangers(15, 16) (commonly referred to as overheater, reoverheater oreconomizer) to which they give up heat to generate steam for remoteheating and/or for actuating one or more turbines for the production ofelectrical energy.

After they have passed through the said convective bank, the vapours,which have a temperature of about 500-600° C., are conveyed to thechimney (60) via a filter array (30) in which any light noncombustedmaterial present in these vapours are processed.

Before entering the said filter array (30), the vapours arising from thesaid convective bank pass through an exchanger (20) in which theypreheat an inlet flow of cold air (21), bringing it to about 250-300° C.

The flow of air thus preheated (22) is fed, via a ventilator (22A) oranother equivalent device, into the burners (12) as separate flows or asa single flow, according to the specific constructional characteristicsof the plant.

A fraction (23) of the flow of preheated air (22) is conveniently mixedwith a flow of cold air (24) in order to form a flow of air (25) atabout 150° C. The said flow of air (25) is fed, through a ventilator(25A), to a mill (45) where it acts as a means of transporting a finelyground coal in which typically 99% of the particles are less than 100mesh and 77% are less than 200 mesh in size.

In order to produce this coal dust, the mill (45) is fed withcoarse-sized coal obtained from a silo (44).

Supply flows (42A) and (43A) of methane and fuel oil, originating,respectively, from a methane gas distribution network (42) and from aheated tank (43) of fuel oil, also arrive at the burners (12).

For simplicity, in FIG. 7 only one system for supplying methane gas,fuel oil and coal dust to the entire array of burners (12) has beenrepresented. Preferably, each burner (12) will, however, be providedwith its own separate supply system.

Naturally, a person skilled in the art will appreciate that the schemerepresented in FIG. 7 has been given purely by way of illustration andthat many other specific forms of plant embodiments can be envisaged,such as, for example, boilers with vapour tubes or with a diathermicfluid, which can be significantly far-removed from the scheme of FIG. 7.Nevertheless, these plants are all compatible with the objectives of thepresent invention since they are capable of achieving instantaneouscombustion.

For the purposes of the present invention, an instantaneous-combustionpower plant also comprises a system (53A) which is capable of feedingthe flame of at least one burner (12) with a flow (53) of NFSF having acontrolled and predetermined particle size.

In relation to the specific technical requirements or to preselectedforms of construction, the flow (53) of NFSF is conveyed by a suitablecarrier fluid (52), typically air, and arrives directly at one or moreburners (12) or at a preselected zone of the boiler, through one or moreindependent adduction tubes. In any case, the boiler zone preselectedfor supplying NFSF according to the present invention will becharacterized by a temperature which is high enough to minimize theamount of non-combusted particles which collect in the hopper (13).Expediently, the said zone is the abovementioned combustion zone (11) inwhich the temperature is preferably at least 1500° C.

Examples of such NFSF supply systems are described earlier withreference to FIGS. 8 and 9.

FIG. 8 shows a mechanical NFSF supply system in which the NFSF, storedin a first silo (40) passes to a blade mill (41) in which it isappropriately ground and then conveyed to a second silo (46) which canalso serve as a receiver tank. The second silo (46) has a moving base in(47) consisting of a conveyor belt which discharges a preselectableamount of NFSF over time into a twin Archimedean screw (48) whichconverges towards the centre. Wheels (49) drive the NFSF towards anArchimedean screw (50) which emits it, through an aperture (51), intothe flow of coal dust carried by the carrier air (25) conveyed to theflame (31) of the burner (12).

The silos (46, 47) are lined with an anti-adhesive epoxy varnish andhave an upper aperture fitted with a movable door to allow theoperations of loading of the product and, at the same time, airtightnesswith respect to atmospheric agents.

The Archimedean screw (50) passes through the air-burner tank (50A),inside which temperatures of about 300° C. are reached. This tank istherefore fitted with a water jacket (not shown) to maintain the NFSF ata temperature below 200° C., since, above this temperature, the NFSFtends to soften and to become sticky, thus making it difficult to supplyto the burner. In addition, the entire Archimedean screw (50) has beenentirely lagged with ceramic fibre.

The Archimedean screw (50) is driven by a first electric motor (50 b)coupled to a reduction unit and has a speed of 140 revolutions/minuteand a carrying capacity of 1200 kg/h.

There are two wheels (49) and these are controlled by a secondelectrical motor (not shown) provided with a reduction unit. The saidwheels (49) are connected together by means of a system (not shown)comprising a trapezoidal belt provided with a screw coupling whichconnects two pulleys of different diameter so as to make the lower wheelrotate at a faster speed than the upper wheel.

FIG. 9 illustrates an alternative pneumatic NFSF supply system, in whichthe NFSF passes from a silo (46) to a blade mill (41) connected to asource (52) of carrier air which, via tubing (54) pneumatically conveysthe NFSF, which has been appropriately ground, to the fire area (11) ofthe boiler (1). At the same time, the coal dust is also fed inpneumatically in a manner entirely similar to that described with regardto FIG. 8.

EXPERIMENTAL SECTION I. Fuel Materials

The non-fossil solid fuel (NFSF) had an average composition of 70% byweight of USW, 15% by weight of non-elastomeric polymer materials(plastic wrapping materials) and 15% by weight of elastomeric polymermaterials (used tyres stripped of the metal carcase and shredded intoparticles less than 5 mm in size).

Before being conveyed to the combustion zone, the said NFSF was driedand ground until all the particles were practically smaller than 1 meshin size and 50% of them were smaller than 4 mesh in size. The apparentdensity of the so obtained NFSF was of about 0.4 g/cm³.

Table 1 below shows the results of the physicochemical analysis of thesaid NFSF and of a South African coal normally used in electric powerstations, in the form of a dust in which at least 70% of the granulesare smaller than 200 mesh in size.

TABLE 1 Dry Dry Results Method coal NFSF Coal (%) ASTM D 76.61 54.115373 Hydrogen (%) ASTM D 3.63 7.13 5373 Nitrogen (%) ASTM D 1.53 1.055373 Sulphur (%) ASTM D 0.63 0.108 4239 Ash (%) ASTM D 10.89 11.99 5142Oxygen (%) calculated 6.71 25.33 Moisture (%) ASTM D — — 5142 Highercalorific power ASTM D 7085 5803 (Kcal/kg) 3286 Lower calorific powercalculated 6899 5392 (Kcal/kg) Volatile substances (%) ASTM D 25.5981.61 5142 Chlorine (%) ASTM D <0.1 0.27 2361 Alpha stoichiometry⁽¹⁾calculated 9.87 7.66 (kg/kg) ⁽¹⁾The term “Alpha stoichiometry” indicatesthe stoichiometric amount of air, by weight, required to burn 1 kg ofthe compound under consideration.

On the other hand, Table 2 below gives the average physicochemicalvalues for natural gas (methane) used in the same plant. The chemicalvalues were determined by gas chromatography.

TABLE 2 Results Methane gas Helium (mol %) 0.04 Methane (mol %) 90.89Ethane (mol %) 4.26 Isobutane (mol %) 0.17 Isopentane (mol %) 0.05Hexanes + higher hydrocarbons (mol %) 0.05 Nitrogen (mol %) 2.92 Carbondioxide (mol %) 0.19 Propane (mol %) 1.15 n-Butane (mol %) 0.24n-Pentane (mol %) 0.04 Higher calorific power (Kcal/SMC⁽²⁾) 9309 Lowercalorific power (Kcal/SMC⁽²⁾) 8400 ⁽²⁾SMC = m³ at 15° C. and at 1.01326bar (atmospheric pressure)

II. Plant

The experimental tests were carried out in an experimental power plant(48 tMW) with instantaneous combustion, which was particularly suitablefor evaluating the properties of the burners and of the fuel materials.

The said plant had the structure illustrated in FIG. 8.

In particular, the boiler in this experimental plant has a horizontalprism-shaped combustion chamber of the twin-drum type and a maximumcapacity of 70 t/h of steam at 29 bar.

In addition, the said combustion chamber is partially refractory so asto control the heat exchange with the flame and to allow an efficientevaluation of the thermal behaviour of a power plant. This chamber alsohas many points of access which allow the observation and measurement ofthe flame along the entire combustion chamber.

The control and regulation system for the plant is of the semi-automatictype and reports, in a control room, all the process data where thesedata are acquired automatically and continuously.

For continuous analysis of the vapours, the plant is equipped with thefollowing analysers:

Siemens IR ULTRAMAT™ S NO_(x) analyser with a scale range from 0 to 800mg/Nmc and equipped with an NO₂/NO converter—precision <0.5%, base scale(b.s.)

Siemens IR ULTRAMAT™ 5 CO analyser with a scale range from 0 to 800mg/Nmc—precision <0.5% b.s.

Siemens IR ULTRAMAT™ 5 CO₂ analyser with a scale range from 0 to20%—precision <0.5% b.s.

Siemens OXYMAT™ 5 paramagnetic O₂ analyser with a scale from 0 to 5%,from 0 to 10% and from 0 to 25%-precision 0.5% b.s.

Siemens IR ULTRAMAT™ 5 SO₂ analyser with a scale range from 0 to 3000mg/Nmc—precision <0.5% b.s.

A suction pyrometer is installed on the bottom wall of the boiler, forthe continuous measurement of the temperature of the vapours leaving thecombustion chamber, before they pass through the convective bank.

An endoscope is installed on the front of the boiler to allow overallmonitoring of the flame produced. A commercial telecamera with an RGBoutlet is mounted on the endoscope eyepiece; the signal is sent to adigital image acquisition system which, with the aid of “imageprocessing” software, analyses the shape of the flames and of thetemperature peaks.

The burners are of the triple-flow and three-fuel “low NO_(x)” type andwere set up to ensure the best operating conditions in terms ofemissions of NO_(x), CO and non-combusted materials in the ash.

The burners are of the circular type and comburent air is divided,around the longitudinal axis of the burner, into three helical flows.

The central primary air (25) also constitutes the fluid for thepneumatic transportation of the coal dust.

The vapour analysis system was integrated by means of a movable stationcapable of sampling dioxins, furans, PAHs (polycyclic aromatichydrocarbons), heavy metals, halohydric acids, etc.

The addition of NFSF to the flow of dust was carried out via a sideinlet (51) already present on the burner and normally used to draw incooling air. No modification of the conventional combustion plant wasthus necessary.

This supply system makes it possible to introduce from 10 to 30% byweight of NFSF into the flow of coal dust without varying the air/coalratio and without giving rise to any appreciable disruptions in thefluid dynamics of the burner.

III. Short-Duration Co-Combustion Tests 1. NFSF/Methane GasCo-Combustion

Two tests each lasting about 15-20 minutes were carried out.

In the first test, the gas flow rate was about 2900 Nmc/h, that of theprimary air was about 9 t/h and that of the NFSF was about 1670 kg/h.

In the second test, the gas flow rate was about 2900 Nmc/h, that of theprimary air was about 9 t/h and that of the NFSF was about 690 kg/h.

As regards the flame behaviour, the visual test made it possible toobserve that:

the discharge of the NFSF from the mouth of the burner was uniform andfinely dispersed, both spatially and over time;

laterally to the flame, there was no obvious presence of NFSF apart fromthe existence of a few particles of burning material slightly downfieldof the mouth of the burner;

the amount of non-combusted material which settled in the hopper placedat the bottom of the boiler was very low (as confirmed later by the ashvalues) and therefore did not concern the first half of the boiler;

the amount of non-combusted material was also low and of smalldimensions at the inlet of the convective bank;

a few particles of material of plastic consistency tended to bedeposited on the glass in the back door.

2. NFSF/Coal Dust Co-Combustion

A test lasting about 30 minutes was carried out.

The flow rate of the coal was about 3 t/h, that of the NFSF was about600 kg/h (about 20% by weight relative to the coal dust) and that of theprimary air was about 9 t/h.

Under these conditions, it was found that:

the coal flame did not make it possible to locate the NFSF leaving theburner, nor in the central zone of the flame;

it was possible to distinguish the NFSF only in the peripheral zones andat the end of the flame;

from the back of the boiler, it was, however, possible to see materialfall into the hopper in similar measure to that found with methane gas.

No appreciable differences as regards the functioning with methane gaswere observed in the complex.

The only item of critical technical data is that in the operation withmethane gas, the temperature of the vapours leaving the combustionchamber were maintained at about 850° C., whereas, in the operation withcoal, this temperature was moderately lower (about 720° C.).

In order to return to a temperature of about 850° C., the flow rates offossil fuel were increased in the following tests.

IV. Long-Duration Co-Combustion Tests 1. Characterization Tests

Before carrying out the co-combustion tests, two tests were carried outwith coal dust alone, in order to gather as much data and measurementsas possible regarding the typical functioning of the plant fed only withcoal dust, in order then to compare them with those of NFSF/coal dustco-combustion.

The duration of the tests were conditioned by the needs for long periodsof sampling to measure the microcontaminants.

In particular, the operations below were carried out in each of the twotests concerned:

sampling of the coal dust in order to determine the relative particlesize distribution curves according to Rosin & Rammler;

vapour analysis (O₂, NO_(x), CO, CO₂, SO₂);

sampling of the particulates in the vapours in order to determine theconcentration of ash and the content of non-combusted materials;

sampling of the heavy ash in order to determine the residual percentageof the starting fuel material and the concentration of non-combustedmaterials;

sampling of the process effluents for the determination of dioxins,furans, PAHs, heavy metals and halohydric acids.

2. Baseline Coal Test

This test was started with a coal load of about 4 t/h, corresponding toabout 33 tMW (100% thermal load of the burner), and with a primary airflow rate of about 9.5 t/h.

The flame produced under these conditions was stable, attached to theburner, of elongated shape, typical of burners with large air “staging”.

The emissions in terms of NO_(x), CO and noncombusted materials in thefly ash are given in FIG. 1, as the amount of excess air changes (O₂% inthe vapours)

The heavy ash (HA) removed from the boiler hopper was characterized andexpressed both in terms of residual percentage relative to the startingfuel material (FIG. 2), and in terms of the non-combusted materials(FIG. 3). These data are given by way of reference to evaluate theresults obtained in the NFSF/coal dust co-combustion.

3. NSFS/Coal Dust Co-Combustion Test

The test was carried out after the boiler had been brought to theoperating conditions, with coal dust alone.

The overall heat input of the co-combustion was equal to that in theabove baseline test: coal=3.6 t/h, NFSF=543 kg/h.

The heat input due to the NFSF was equal to about 10% of the total 33tMW, while the NFSF/coal weight ratio was 15%.

The flame produced under these conditions did not differ substantiallyfrom that obtained with coal alone. It was stable, attached to theburner and the flame reading signal (CCRT FLUX 3900 model, IR) did notexperience any changes. The presence of the NFSF was detected only byparticles of material which continued to burn even outside the flame, inthe final path of the combustion chamber.

The emission values for NO_(x), CO, non-combusted materials in the flyash and SO₂, obtained as the amount of excess air changes (O₂% in thevapours), is given in FIGS. 4 and 5, together with the data recordedduring the baseline combustion.

The heavy ash (HA) collected in the boiler hopper was characterized andexpressed in terms of residual percentage relative to the starting NFSF(FIG. 2). The non-combusted materials were of the order of 30-40%,compared with 5% recorded in the previous baseline test (FIG. 3).

At the end of the abovementioned test, while the boiler was in operatingmode, the remaining NFSF was burnt, thus carrying out anothershort-duration test with a higher flow rate of NFSF. In this test, whilestill keeping the total heat input equal to about 33 tMW, the flow rateof NFSF was 774 kg/h, corresponding to an NFSF/coal weight ratio ofabout 24% and a heat input of about 15%.

The results obtained in terms of heavy ash and non-combusted materialsare given in FIGS. 2 and 3.

V. Evaluation of the Results

The amount of heavy ash produced in baseline mode with coal alone was0.71% relative to the coal fed in, whereas the coal/NFSF co-combustiontest gave a heavy ash value of 2.53% relative to the entire fuelmaterial introduced (coal+NFSF).

The CO values show no significant changes (FIG. 4) and the slightincrease found in the case of co-combustion (coal+NFSF) is dueessentially to the small excess of air used.

Even for NO_(x), the values are essentially the same (FIG. 4). Theslight shift encountered in the co-combustion with NFSF falls within theresults dispersion range and confirms that the formation of thismicrocontamination can essentially be attributed to the coal. The amountof fly ash formed can also essentially be attributed to the amount ofburnt coal (FIG. 6). The NFSF apparently produces no fly ash.

The non-combusted. material values in the fly ash in coal/NFSFco-combustion were a few percentage points lower than those obtained inthe baseline test.

Lastly, the conclusions which can be drawn following the abovementionedtests are that:

the co-combustion of an instantaneously combusting fossil fuel with NFSFis possible in the normal burners installed in power plants withoutneeding to make particular modifications to these burners;

the NFSF behaves like a common instantaneously corn-busting solid fuelof moderate calorific power;

efficient grinding and/or shredding of its components reduces the levelof non-combusted materials both in the heavy ash and in the fly ash,bringing it to levels similar to those of the instantaneously combustingfossil fuel burnt together with NFSF;

the NO_(x) and CO levels are comparable with those of the fossil fuelburnt together with NFSF;

by virtue of the smaller sulphur content of the NFSF relative to coal,the SO₂ levels are proportionately lower;

there are no dioxins or furans present;

the PAHs are of the same type and at the same level as those which canbe found with coal alone;

the level of halohydric acids and inorganic micro-contaminants reflectsthe analytical composition of the NFSF;

heavy ash is predominant in the case of NFSF, while fly ash ispredominant in the case of coal. On the one hand, the increased amountof heavy ash makes its extraction system more burdensome to manage, butthis drawback is largely compensated for by the lower presence of flyash which passes through the combustion chamber and, on reaching theconvective bank, adhere to, soil, corrode, erode and reduce the heatexchange, thereby making it necessary to carry out frequent cleaning,preferably by blowing. Moreover, the fly ash which is not stopped by theconvective bank comes to the filters and thus increases the frequency ofinterventions required to remove them.

1. A fuel composition, comprising: from 60 to 95% by weight of a fossilfuel; and from 40 to 5% by weight of a non-fossil solid fuel includingurban solid waste, and at least a further component selected from thegroup consisting of elastomeric polymer materials, non-elastomericpolymer materials and mixtures thereof, wherein at least 90% by weightof the fuel composition fed into a burner is combusted in less than 10seconds.
 2. A composition according to claim 1, in which the amount ofsaid fossil fuel is between 60 and 80% by weight.
 3. A compositionaccording to claim 1, in which the amount of the said non-fossil solidfuel is between 40 and 20% by weight.
 4. A composition according toclaim 1, in which the fossil fuel is selected from the group consistingof methane, fuel oil, fossil coal dust, and mixtures thereof.
 5. Acomposition according to claim 1, in which the non-fossil solid fuel hasan apparent density equal to or less than 0.6 g/cm³.
 6. A fuelcomposition, comprising: from 60 to 95% by weight of a fossil fuel; andfrom 40 to 5% by weight of particles less than 1 mesh in size of anon-fossil solid fuel including urban solid waste, and at least afurther component selected from the group consisting of elastomericpolymer materials, non-elastomeric polymer materials, and mixturesthereof, wherein at least 90% by weight of the fuel composition fed intoa burner is combusted in less than 10 seconds.
 7. A compositionaccording to claim 6, in which at least 90% by weight of the particlesare smaller than 2 mesh in size.
 8. A composition according to claim 6,in which at least 50% by weight of the particles are smaller than 4 meshin size.
 9. A composition according to claim 6, in which the particlescomprise non-elastomeric polymer material of less than 5 mm in size. 10.A composition according to claim 6, in which the amount of said fossilfuel is between 60 and 80% by weight.
 11. A composition according toclaim 6, in which the amount of said non-fossil solid fuel is between 40and 20% by weight.
 12. A composition according to claim 6, in which thefossil fuel is selected from a group consisting of methane, fuel oil,fossil coal dust and mixtures thereof.
 13. A combustion methodcomprising the steps of: feeding the flame of a burner of aninstantaneous-combustion boiler with a flow of fuel compositionincluding: from 60 to 95% by weight of an instantaneously combustingfossil fuel; and from 40 to 5% by weight of a non-fossil solid fuel madeof urban solid waste and one or more other materials selected from thegroup consisting of elastomeric polymer materials, non-elastomericpolymer materials, and mixtures thereof, which has been suitably treatedso as to be instantaneously combustible; combusting at least 90% byweight of said fuel composition fed into the burner in less than 10seconds.
 14. A combustion method according to claim 13, in which thesaid non-fossil solid fuel consists of particles less than 1 mesh insize.
 15. A combustion method according to claim 14, in which at least90% by weight of said particles are less than 2 mesh in size.
 16. Acombustion method according to claim 14, in which at least 50% by weightof said particles are less than 4 mesh in size.
 17. A combustion methodaccording to claim 14, in which said particles comprise elastomericpolymer particles of less than 5 mm in size.
 18. A combustion methodaccording to claim 13, in which the instantaneously combusting fossilfuel is selected from a group consisting of methane, fuel oil, fossilcoal dust, and mixtures thereof.
 19. A combustion method comprising thesteps of: feeding a fuel composition into a zone of a boiler, said zonehaving a predetermined temperature value and said fuel compositionincluding: from 60 to 95% by weight of at least one instantaneouslycombusting fossil fuel, and from 40 to 5% by weight of at least oneinstantaneously combusting non-fossil fuel including urban solid waste,and at least one further component selected from the group consisting ofelastomeric polymer materials, non-elastomeric polymer materials, andmixtures thereof; combusting said fuel composition in said boiler suchthat at least 90% by weight of the fuel composition is combusted in lessthan 10 seconds, and generating an amount of heavy ash from saidcombustion step, wherein said predetermined temperature value isselected so that non-combusted materials are contained in said amount ofheavy ash in an amount of less than 50% by weight.
 20. A combustionmethod according to claim 19, in which said zone of the boiler intowhich said non-fossil fuel is fed has a temperature of not less than1500° C.
 21. A combustion method comprising the steps of: feeding aboiler with a fuel composition including: from 60 to 95% by weight of aninstantaneously combusting fossil fuel, and from 40 to 5% by weight ofan instantaneously combusting non-fossil fuel including urban solidwaste, and at least one further component selected from the groupconsisting of elastomeric polymer materials, non-elastomeric polymermaterials, and mixtures thereof, combusting said fuel composition insaid boiler such that at least 90% by weight of the fuel composition iscombusted in less than 10 seconds, generating an amount of heavy ashfrom said combustion step, wherein said non-fossil fuel has apredetermined particle size so that non-combusted materials arecontained in said amount of heavy ash in an amount of less than 50% byweight.
 22. A system for combusting, comprising: a fuel compositioncomprising from 60 to 95% by weight of at least one instantaneouslycombusting fossil fuel, and from 40 to 5% by weight of at least oneinstantaneously combusting non-fossil fuel including urban solid waste,and at least one further component selected from the group consisting ofelastomeric polymer materials, non-elastomeric polymer materials, andmixtures thereof, a boiler having at least one burner, a system forsupplying said at least one burner with a flow of said at least oneinstantaneously combusting fossil fuel carried by a carrier fluid, and asystem for feeding said at least one instantaneously combustingnon-fossil solid fuel into said flow, wherein said system for combustingand said fuel composition are configured such that at least 90% byweight of said fuel composition is combusted in less than ten secondswhen said fuel composition is fed into said boiler.
 23. A system forcombusting, comprising: a fuel composition comprising from 60 to 95% byweight of at least one instantaneously combusting fossil fuel, and from40 to 5% by weight of at least one instantaneously combusting non-fossilfuel including urban solid waste, and at least one further componentselected from the group consisting of elastomeric polymer materials,non-elastomeric polymer materials, and mixtures thereof, a boilercomprising at least one burner and at least one fire area, a system forsupplying the fire area of said boiler with a flow of said at least oneinstantaneously combusting fossil fuel carried by a carrier fluid, and asystem for conveying said at least one instantaneously combustingnon-fossil fuel into the fire area of said boiler, wherein said systemfor combusting is configured such that at least 90% by weight of saidfuel composition is combusted in less than ten seconds when said fuelcomposition is fed into said boiler.